Silicone rubber compositions cure to give silicone rubbers that exhibit a desirable modulus, an excellent heat resistance, an excellent water resistance, and so forth, and for these reasons are used for sealing members such as gaskets, packings, and O-rings. Silicone rubber compositions may be broadly categorized into millable silicone rubber compositions and liquid silicone rubber compositions and into peroxide-curable silicone rubber compositions and addition reaction-curable silicone rubber compositions.
The following have been introduced in pursuit of an improved resistance to lubricating oil: an addition reaction-curable silicone rubber composition that contains a silicone oil and is intended for gasket applications—refer to JP 05-005064 A (Patent Document 1); a sealing element for waterproof connectors, that is produced from a millable silicone rubber containing a phenylsilicone oil—refer to JP 07-130424 A (Patent of silicone oils—refer to P 2002-338809 A (Patent Document 3) and JP 2004-075813 A (Patent Document 4).
The silicone rubber composition described in JP 05-005064 A (Patent Document 1) is intended for application to gaskets that are continually immersed in a lubricating oil, and as a consequence the cured silicone rubber product therefrom has an overly high hardness. As a result, when this silicone rubber composition is molded into a through hole-containing sealing member and, for example, a metal terminal, metal wire, rubber-coated metal wire, or plastic-coated metal wire is repeatedly inserted into the through hole in the air, the silicone rubber around the through hole is prone to become damaged, i.e., an ability to resist damage is not present.
The oil bleeding-type sealing element for waterproof connectors described in JP 07-130424 A (Patent Document 2) comprises a millable silicone rubber that contains a phenylsilicone oil and exhibits an excellent surface lubricity. However, in the case of a through hole-containing sealing element, the insertion of, for example, a metal terminal, metal wire, rubber-coated metal wire, or plastic-coated metal wire into the through hole readily causes damage to the silicone rubber around the through hole, i.e., a poor ability to resist damage is exhibited.
The oil bleeding-type silicone rubber compositions described in JP 2002-338809 A (Patent Document 3) and JP 2004-075813 A (Patent Document 4) provide cured silicone rubber products that exhibit an excellent surface lubricity. However, when these silicone rubber compositions are molded into a through hole-containing sealing member and, for example, a metal wire, rubber-coated metal wire, or plastic-coated metal wire is repeatedly inserted into the through hole, the silicone rubber around the through hole is prone to become damaged, i.e., the ability to resist damage is inadequate.
When the silicone rubber around a through hole becomes damaged, water, dust, and contaminated air can then easily infiltrate through the damaged area, which results in a reduced sealing performance.